A review of the classic DC-3 and the Handley Page HP.42 yielded a surprisingly close match in empty and max gross take off weight at around 18,000 and 28,000 lbs for the HP.42 and 16,000 lbs and 25,000 for the DC-3. The HP.42 cruised at 87 knots on around 4x500 hp, and the DC-3 at 180 knots on 2x1200 hp. The HP.42 was a lower aspect biplane, the DC-3 a graceful mono plane, the epitome of aviation advances for that era but...
Questions: How much of the DC-3's speed increase was the result of improved engine/prop efficiency? How much from the DC-3's speed increase came from its beautiful Prandtl inspired wing? How much from retracting its gear? How much closer would the HP be with those improvements, while remaining a biplane (perhaps with improved struts)?
I do not expect an exact answer, I am more interested to see how the numbers were crunched and a short explanation why. Thanks.